This invention relates to adaptive filters such as may be used in adaptive array signal processing arrangements.
Sinusoidal interference corrupting a signal is typically eliminated with a fixed notch filter turned to the frequency of the interference. A very narrow notch is usually desired in order to filter out the interference without distorting the signal. However, when the frequency of interference is unknown or drifts with time then the best solution is one which identifies the frequency or frequencies of interference and adapts one or more notches to cancel it. This may be achieved by means of an adaptive notch filter. In a broad RF band, any interfering carrier, modulated or unmodulated, can usually be considered to be narrow band, and an adaptive notch filter will be able to cancel it. However, the wanted signal is generally indistinguishable from the interference and will also be cancelled.